ω-conotoxin CVID inhibits a pharmacologically distinct voltage-sensitive calcium channel associated with transmitter release from preganglionic nerve terminals

Abstract

Neurotransmitter release from preganglionic parasympathetic neurons is resistant to inhibition by selective antagonists of L-, N-, P/Q-, R-, and T-type calcium channels. In this study, the effects of different ω-conotoxins from genus Conus were investigated on current flow-through cloned voltage-sensitive calcium channels expressed in Xenopus oocytes and nerve-evoked transmitter release from the intact preganglionic cholinergic nerves innervating the rat submandibular ganglia. Our results indicate that ω-conotoxin CVID from Conus catus inhibits a pharmacologically distinct voltage-sensitive calcium channel involved in neurotransmitter release, whereas ω-conotoxin MVIIA had no effect. ω-Conotoxin CVID and MVIIA inhibited depolarization-activated Ba2+ currents recorded from oocytes expressing N-type but not L- or R-type calcium channels. High affinity inhibition of the CVID-sensitive calcium channel was enhanced when position 10 of the ω-conotoxin was occupied by the smaller residue lysine as found in CVID instead of an arginine as found in MVIIA. Given that relatively small differences in the sequence of the N-type calcium channel α1B subunit can influence ω-conotoxin access (Feng, Z. P., Hamid, J., Doering, C., Bosey, G. M., Snutch, T. P., and Zamponi, G. W. (2001) J. Biol. Chem. 276, 15728-15735), it is likely that the calcium channel in preganglionic nerve terminals targeted by CVID is a N-type (Cav2.2) calcium channel variant.